SKY-MAP.ORG / WIKISKY

Black Holes
A black hole is defined to be a region of space-time where escape to the outside universe is impossible. The outer boundary of this region is called the event horizon. Nothing can move from inside the event horizon to the outside, even briefly, due to the extreme gravitational field existing within the region.

Big Bang
In physical cosmology, the Big Bang is the scientific theory that the universe emerged from a tremendously dense and hot state about 13.7 billion years ago. The theory is based on the observations indicating the expansion of space (in accord with the Robertson-Walker model of general relativity) as indicated by the Hubble redshift of distant galaxies taken together with the cosmological principle.

Extraterrestrial Life
Extraterrestrial life is life that exists and originates outside the planet Earth, the only place in the universe currently known by humans to support life. Its existence is still hypothetical as there is currently little, if any, evidence of other planets that can support life, or actual extraterrestrial life that has been widely accepted by the scientific community.